Marrying her before taking Westeros also draws unfortunate parallels to the Prince of Dragonlies and a certain disaster known as Jenny of Oldstones, and would thus net us fewer houses when we invade, since its a moderate (but not lethal) modifier.
Due to the sheer quantity of Houses and keeps in Westeros, I'm expecting DP to handle the 'rebelling' houses during the Civil War in bulk, possibly by Region. No way he simulates each and every one of the bazillion houses strewn around the Reach, Riverlands, Crownlands, etc etc etc etc, beyond houses we have personally diplomanced or those who are canonically important or otherwise noteworthy in one way or another (like the Darry's or Florents).
So for example, generic Crownland Houses which we haven't diplomanced and have also not been courted by the Lannisters could have something like this, where DP tosses a d100 and if they get more than 70 declare for us, less than 30 for the Lannisters, and in between the old classic of 'What Civil War? I haven't received any ravens..."
Modifiers for House Generic of Generic Crownland Place:
Historical ties to Targs: +30
Rumors of blood sacrifice: -10
Mistreated by Lannisters/Baratheon regime: +15
She married a smallfolk?! *Jenny of Oldstones collective PTSD activated*: -12
Just spitballing here to get my point across. Thing is, something like a new Jenny of Oldstones is, unlike blood sorcery, something Westerosi lords can imediately grasp and comprehend, and won't be too fond off. Not a deal breaker, but not something too minor, hence -12, though it could vary from -5 to -20 depending on how DP is playing Westerosi sensibilities. The thing I'm trying to explain here is that marrying her before the invasion may (will, statistically) tip some houses on siding against us.
Now, I'm also operating under the assumption that we want to minimize bloodshed in Westeros, but if the intent is the opposite (how much nobility do we need to trim so the class as a whole is weak enough to only put up token resistance to the magitech revolution? How many empty keeps to we need/want?) then marrying her is a good move.
